Add full multi-operation transaction explanations with backward compatibility

[phertyameen]

closes #509

Summary

Implement support for explaining all supported Stellar operation types and return a structured operations[] array for every transaction.

Changes

• Added explainers for:
  • create_account
  • change_trust
  • set_options
  • account_merge
  • manage_sell_offer
  • manage_buy_offer
  • path_payment_strict_send
  • path_payment_strict_receive
  • payment (existing support retained)
• Added graceful fallback explanations for unsupported operation types.
• Updated transaction responses to include ordered operations[] with index, type, summary, and details.
• Preserved payment_explanations for backward compatibility.
• Updated skipped_operations to count only truly unsupported operations.
• Added Horizon mappings and operation enum variants.
• Added unit tests for all supported operation types.

Result

Multi-operation Stellar transactions are now fully explained in order, while existing consumers remain compatible with the legacy payment_explanations field.

[Tinna23]

@phertyameen please fix CI

[phertyameen]

@Tinna23 fixed